1. Field of the Invention
The present invention relates to an electric projection screen roller and balance rod assembly. More particularly, the present invention is directed to an electric projection screen roller and balance rod assembly that is provided in a protective housing and included a screen roller assembly and a screen balance rod assembly, so as for the upper end section of a projection screen to be firmly secured to the roller assembly and the lower end section of the projection screen to be firmly secured to the balance rod assembly.
2. Description of the Related Art
Various activities to pass on knowledge and information are frequently held in modern times. Projectors are widely used as auxiliary teaching tools in most teaching activities. Accordingly, a projection screen is indispensable for showing the projected content from the a projector.
While being used, referring to FIGS. 1,2 and 3, an electric projection screen housing 10 containing a scroll of projection screen 20 must be secured to a wall first, and the projection screen 20 together with a balance rod 50 unwinds from a roller 30 to descend below the housing 10 to a lowered, viewing arrangement or winds around the roller 30 to a raised, storage position depending on the rotation of the roller 30 performed by an electrically powered motor.
A conventional projection screen roller 30 does not be provided with any structure for securing one end section of the projection screen 20, but a piece of tape 40 is adhered on a predetermined surface position of the roller 30 for the upper end section of the projection screen 20 to be secured thereto.
Referring to FIGS. 4, 5 and 6, the lower end section 201 of the projection screen 20 is clamped by a balance rod 50, which serves as a suspended weight so as to cause the projection screen 20 to descend or raise in a relatively planar configuration as it unwinds from or winds around the roller 30, and the projection screen 20 can be kept stable while being applied.
While the balance rod 50 being assembled, two pieces of thick paperboard A are provided to clamp the lower end section 201 of the projection screen 20 and then stapled to firmly assemble therewith, the lower end section 201 of the projection screen 20 together with the pieces of paperboard A is inserted in the balance rod 50, and two endcaps 60 are respectively provided to cover both ends of the balance rod 50.
Although the above-mentioned conventional projection screen roller and balance rod can respectively secure the upper and lower end sections of the projection screen 20, there are the following drawbacks in the conventional projection screen roller and balance rod after being used for a period of time:                1. The tape 40 adhered on the surface of the roller 30 will lose stickiness after contacting with the projection screen 20 for a period of time, so that the upper end section of the projection screen 20 will easily separate from the roller 30.        2. Because of the changes of temperatures, the tape 40 adhered on the surface of the roller 30 will lose stickiness after being used for a period of time, so that the upper end section of the projection screen 20 will easily separate from the roller 30.        3. It is troublesome and wastes time for the lower end section 201 of the projection screen 20 to be clamped by pieces of paperboard A and fixed by staples before being assembled with the balance rod 50, and it is easily to cause wrinkles on the projection screen 20 fixed by means of staples.        4. The projection screen 20 must be cleaned by water after being used for a period of time, and the pieces of paperboard A are easily wetted and worn. It is troublesome to replace new paperboard.        5. It is troublesome and wastes time for the lower end section 201 of the projection screen 20 to be clamped by pieces of paperboard A before being inserted in the balance rod 50, and it is also troublesome that the thickness of the pieces of paperboard A must accord with the groove size of the balance rod 50.        